The goal of this proposal is to establish a well-characterizes rat model of hepatocellular carcinoma which can be use in studies on the interaction between progressive neoplastic disease and the host immune system. The model system to be established involves the use of a substrain of Fisher 344 rats (called the German Fisher 344 rat) which lacks an enzymatically active form of dipeptidyl peptidase IV (DDPIV). DDPIV is a cell surface exoprotease normally expresses by hepatocytes, biliary duct cells, activated T-cells, pancreatic ducts and a host of other tissues. The cellular function of DPPIV is unclear, however, the lack of enzymatically active DPPIV in German Fisher rats has no untoward effect on the development or well-being of these animals. This deficiency will be exploited by using German DDPIV-rats as hosts for DPPIV+ transplantable tumor cell lines and preneoplastic cell populations isolated from American Fisher rats undergoing chemically induced hepatocarcinogenesis. The advantage of using enzymatically active DPPIV as a tumor marker is that donor-derived tumors present in the German rat liver can be identified as well as quantitated using antibodies and enzyme assays specific for the active form of DPPIV. The specific aims of this proposal are: 1). To develop and optimize methods for the quantitation of tumor burden. Enzymatic and immunological assays for DPPIV will be used to provide a definitive measurement of tumor burden in host tissues. 2). To establish a reproducible model of transplantable hepatocellular carcinoma in the Fisher 344 rat. Several cell lines of hepatocellular carcinoma have been developed in the American Fisher rat that are suitable for transplantation into the livers of recipient German rats. For each cell line included in these studies, an optional inoculum of donor tumor cells will be determined that results in a predictable and incidious course of hepatic neoplastic disease following injection through the portal veil. 3). To develop probes for the enzymatically inactive form of DPPIV. Monoclonal antibodies specific for the truncated form of DPPIV expressed by German rats will increase the flexibility, sensitivity and accuracy of measurements of tumor burden by providing a dual marker system that will recognize both DPPIV+ as well as DPPIV-tumor cells. This reagent will also extent the transplantation model by permitting exchange and detection of donor cells between both substrains of rat. 4). To develop immunological methods for the re-isolation and fractionation of tumor cells. A panel of monoclonal antibodies is presently available which can identify antigens present on normal hepatocytes, oval cells, preneoplastic as well as neoplastic tumor cells. A given tumor nodule is usually comprised of subpopulation of these cells. Dissection and isolation of these cells from tumor nodules will provide and animal model in which immune interactions can be determined for each component tumor cell type.